Originally Posted by vwfreak
Let me start by saying I am fairly novice at auto repair and I won't pretend to know more than I do.
With that out of the way here's my issue: I have a 1991 VW Jetta, 1.8 L automatic with 125k miles. All the recommended maintenance is completed at the recommended intervals. For the past few days, when I start my car (after sitting for more than four hours), the engine revs itself four or five times usually from idle to 1500-2000 RPM then smooths out. If the car hasn't been sitting long, this doesn't happen.
Being a novice, I checked the rotor and distributor cap. I noticed some build-up so I changed them (my level of know-how
) even though they only have under 10k on them. No difference was made. I am wondering whether changing the plugs and the cables will do anything or I'm barking up the wrong tree.
Please advise other diagnostics I might run. Thanks!
Not likely an ignition problem. Sounds suspiciously like a vacuum leak that goes away. First try looking at the auxilary air regulator. It is essentially a device that gives you a controlled vacuum leak to raise idle speed during warm-up (very rough description). Also look at the intake duct between the airflow sensor and the throttle body. Check specifically for cracks on the underside. Any leak here can cause this to occur also.
If you don't have a manual get one now, it'll show you where the aux regulator is and how to test it. Robert Bentley is the best for VW's, they made the factory service manuals. At least pop for a Haynes manual. For your car you need #884, probably around $15 at your friendly local parts house.
Good luck and let me know what you find.